The present invention relates to changing forward and reverse tape travelling directions in a video tape recorder (VTR) for domestic use.
According to a conventional construction of a VTR, as described in Japanese Utility Model Publication No. 60-17073, a back tension servo mechanism is turned OFF when a magnetic tape is to travel in a direction opposite to a normal or forward travelling direction of the tape. Such conventional VTR for domestic use merely intended to reproduce a recorded picture at the same magnetic tape travelling speed as that used in the recording of the picture.
However, according to the recent technical trend on VTR's for domestic use, it is required to project a special recorded picture on a television set in a noiseless state, and it is also required to perform a highly accurate retrieval of a recorded picture position as quickly as possible at the time of copying recorded contents of a magnetic tape after recording onto another magnetic tape, namely, at the time of performing a so-called dubbing.
It is becoming difficult for the prior art to satisfy such requirements. More particularly, the separating of a tension pole of the back tension servo mechanism from a magnetic tape at the time of reverse travel of the tape, gives rise to the necessity of again operating the back tension servo mechanism at the next time of reverse travel. Therefore, it is difficult to appropriately control the tension of the magnetic tape in forward tape travel and in reverse travel.
In a special reproduction, for example in a generally called slow-motion reproduction, by allowing a magnetic tape to travel intermittently, it is made possible to trace a predetermined recording track using a magnetic head, to obtain a clear picture. However, at the time of change between the forward and reverse travel of the tape in such intermittent tape travelling, it is difficult to control the tension of the magnetic tape.
In the prior art described above, no consideration is given to an appropriate control for the tension of a magnetic tape at the time of change between the forward and reverse tape travel directions. Particularly, when there is a change from one to the other tape travelling direction in the intermittent tape travelling, the magnetic tape is instantaneously loosened, thus causing a poor contact between the magnetic head and the magnetic tape, that is, creating a space loss, with the result that the reproduced picture contains noise and is unsightly.
Moreover, the time period required for the direction change is long and a considerable time period is required for dubbing and editing the magnetic tape.
According to a method proposed for remedying such drawbacks of the prior art, a motor only for driving a reel is used to enhance the control of the tape travel. However, the product obtained is fairly expensive so is not applicable to a domestic VTR.